Re: (ICMP attacks against TCP) (was Re: HPSBUX01137 SSRT5954

[Dana Hudes <dhudes () hudes org>]

you will find a range of MTU sizes in radio links of various sorts which 
is not just 802.11 but also cellular including GPRS CDMA and WCDMA.
Now, in many instances there is a proxy between the mobile station and the 
public network. In fact I wrote a powerpoint presentation summarizing such 
a paper on transparent TCP proxy in WCDMA and its on my site 
http://www.networkengineer.biz  (I took a course in wireless 
architecture).


On Thu, 21 Jul 2005, Darren Reed wrote:

> In some mail from Fernando Gont, sie said:
> > At 07:25 p.m. 20/07/2005, Darren Reed wrote:
> >
> > > In some mail from Fernando Gont, sie said:
> > > > The IPv4 minimum MTU is 68, and not 576. If you blindly send packets 
> > > larger
> > > > than 68 with the DF bit set, in the case there's an intermmediate with an
> > > > MTU lower that 576, the connection will stall.
> > >
> > > And I think you can safely say that if you see any packets trying to
> > > indicate that the MTU of a link is "68" then you should ignore it.
> >
> > Yes. But what about 296?
> ...
> > > I think it is reasonable to say anyone trying to advertise an MTU less
> > > than 576 has nefarious purposes in mind.
> >
> > There are still some radio links with MTUs of 296 bytes.
>
> Go search with google....people still actively use smaller MTUs.
>
> What do you do?  Where do you draw the line in the sand?
>
> Darren